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Disa (pronounced DEE-za) is a genus of approximately 162 species of terrestrial orchids native to Africa. The mere handful of easily cultivated Disas we will discuss here, are native to southern Africa, and in particular, South Africa and the area of Table Mountain, which overlooks the city of Cape Town. The brilliant scarlet Disa uniflora is known as "The Pride of Table Mountain". In South Africa, the genus is pronounced "DYE-za," but either way, they are delightful plants. |
 In nature,
the Disas can be found in the Fynbos, a unique, arid,
scrub forest found no where else in the world. They grow along
cold mountain streams of very pure, acidic water, in moss and
among roots on rocks, and on cliff faces, near waterfalls and
along seeps, always with their "feet" wet. During the
summer, they experience warm sunny days and chilly nights, and
while day temperatures might approach 90F, their roots stay very
cool, never above 70F. During the winter, they experience daytime
temps in the 50's and 60'sF, and night temperatures might get
down close to freezing, with an occasional temporary snowfall.
All of the species require bright light in order to grow and
flower well. |
 The
plants have a definite cycle of growth, bloom, and dormancy.
They produce herbaceous "tufts" of broad, grass-like
leaves arising from a tuber, which lasts only one year. If conditions
are not quite right, a tuber may not be produced, and this plant
usually does not bloom. However, most Disas produce numerous
rhizomes, which start many new plants, often forming whole "mats"
of plants from the same clone. Many of the species and hybrids
bloom from May through August in the Northern Hemisphere, which
corresponds to November through February in the Southern Hemisphere,
including their native South Africa. The blooms last up to six
weeks and generally make excellent cut-flowers for the florist
trade. After blooming, the bright green growths begin to decline,
but that does not mean the plant is dying. The old growths will
begin to yellow and brown off, but meanwhile, many new "baby"
growths are starting to spring up, and cultivated plants will
often have new growths emerging from the drain holes in the base
of the pots. By late Fall, the plants should be transplanted
into fresh potting medium, and this usually means splitting each
plant into several new ones. Thus, a collection of Disas
can double or triple each year just by repotting. |
| The Disa potting media of choice, should be one that does not rot when kept wet, is slightly acidic, and can stay moist and still admit a lot of air without packing down tightly. Many of the expert Disa growers in South Africa, New Zealand, and California are currently getting great results with a mixture of screened New Zealand sphagnum moss leaves and perlite. Others have long used a mixture of peat moss, perlite, and vermiculite. |
 This
is Disa uniflora, the largest flowered of the genus,
with blooms of four to five inches across, making it the mainstay
of most hybridizing. Don't let the name "uniflora"
fool you, the plant often produces three to six flowers per stem.
The first Disa hybrid was registered in 1891, and now
there are over 200 man-made hybrids, with many more added each
year. Disas are protected plants in South Africa and it
has always been difficult to obtain plants. Interest in growing
them has greatly increased just since the 1980's and now some
of the species and the hybrids can be obtained in the United
States. Disa breeding has concentrated mostly on five
species: uniflora, tripetaloides, cardinalis, racemosa, and
aurata. Other less common species are now being employed.
The goal, as in most orchid breeding, is to intensify colors,
increase the flower count, and make the plants easier to grow.
Disa uniflora, of course, adds size and its brilliant
color to its hybrids. Disa tripetaloides is a tiny white
to light pink flower produced in great multitudes. (Remember
the outcome of breeding these two plants, producing Disa Kewensis
in the photograph above.) Disa aurata, until recently,
was considered a bright yellow form of Disa tripetaloides
and helps produce many-flowered orange and yellow hybrids.
Disa cardinalis and racemosa also produce numerous
flowers and help produce blood-red to pink colored hybrids. New
white and yellow variants of these species are being found, and
a couple of blue species, and oddly shaped ones are currently
being added to breeding programs to produce new colors. |
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In nature, Disas are usually pollinated by butterflies, and Disa uniflora, is pollinated by one strongly attracted to red. Anyone visiting the flowers en situ in South Africa, wearing something red, will soon have a cloud of these butterflies surrounding them. When the butterfly visits the Disa flower, the large pollinia become attached to its thorax, directly in front of the legs. At the next flower, the pollen grains are easily brushed onto the surface of the stigma, pollinating the flower. Disas produce seed very quickly, and after pollination, the seed capsule usually matures and splits open at five to six weeks. You can actually pollinate a cut-flower Disa in a vase and the seed capsule will mature before the remaining flowers fade. The seeds can then be sown in sterile flasks, similar to other orchids, or sown on moist, sterile sphagnum moss, peat moss, or sand. |
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So, how does one go about growing Disa orchids? I've outlined the growing conditions they require: Bright light, cool roots, pure water, and very little fertilizer. Anyone living in a mild climate can grow Disas fairly easily. The US west coast, north of San Francisco, seems to be ideal for growing them outdoors most of the year, and many excellent Disa growers are located there. If you live in a warm climate, you can still grow Disas, but you may have to work at it a little. I live in middle Tennessee, where the summer heat often approaches 100F, and can stay above 90F for a month or more, and the nights here may only get as low as 80F for many weeks. Needless to say, I have to work at it a lot, especially since my only growing area is the warm greenhouse. But, these plants are worth the effort. Some growers and botanical gardens resort to air-conditioning the growing area. Whether this is a greenhouse or indoors under lights, they attempt to keep the air temperature well under 80F. Unfortunately, the air-conditioning removes vital humidity from the air, which must be replaced with fogging. This can be an expensive proposition, and I have not found it necessary. My method was to invent a way to simply cool the water which is used to keep the roots moist. This took some experimenting, and a couple of dead-ends, but eventually I came up with a system that works very well and actually takes very little effort, once it is set up. |
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A TDS (total dissolved solids) meter is a must. Disa roots are very sensitive to minerals dissolved in their water, and you cannot get away with "guessing" for very long. An inexpensive TDS meter can be found on the internet for as little as $15. The cheap ones are not accurate but are close enough to be of some help. Start with clean rainwater or RO (reverse osmosis) water. RO water will be about 5 ppm (parts per million dissolved solids) and rainwater, depending on where you live, averages about 20 ppm (mostly from air-born dust). This will do for all your watering needs. But, you will also need to fertilize the plants occasionally, and this is where the TDS meter is most handy. Disas should be fertilized only while actively growing, which may occur as early as mid-winter, and continue until mid-summer. It should always be done very lightly. Add a balanced fertilizer to the water until the TDS is about 100 to 150 ppm. It won't take very much...about 1/8 teaspoon fertilizer per gallon of water. Water the plants with this fertilizer solution, let them sit for a few hours, and then go back and water again with pure water. Rainwater usually has a moderately acid pH of 5 to 5.6, which is perfect for Disas. Addition of fertilizer may lower the pH even more, which is OK. Using a groundwater source should be avoided because of a normally alkaline pH of 7.2 to 8.0, and a high TDS level, often 300 to 800 ppm. Municipal water may also be harmful because Disas are sensitive to both the chlorine and floride treatments. |
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Because the Disa's roots are always wet, many growers have a problem battling root rot due to fungus infection, especially during the winter. A monthly dose of Cleary's 3336 systemic fungicide eradicates nearly all of this problem. Pests to watch out for include mealy bugs, thrips, aphids, and spider mites. I use a spray and drench solution of Orthene soluable crystals to kill any insects on my other orchids, and by keeping the humidity high, the spider mites are kept under control. I havn't had many insect problems on my Disas. The first year, I had aphids come in and find a nice home on the flower buds. The Orthene quickly took care of that, and now I routinely treat the Disas as I'm spraying my other orchids. |
| To see photos of various Disa flowers, click this link. |
| My New Disa growing tray as of summer 2004. Click this link to see how I built it |
| If you would like to learn more about Disa orchids, or want more details about my "freezer set-up", feel free to contact me at: emerkle@merklesorchids.com You should also visit the websites of a couple "Disa Buddies" of mine. These guys are just crazy about Disas and they have many really great plants, and have started their own quality breeding programs. |
This is Disa Kewensis, a man-made
hybrid of two species, Disa uniflora and Disa tripetaloides.
The delicate beauty and uniqueness
of these special orchids is why we have given them their own
page on our website.
Disa
flowers are built a little differently than many orchid flowers,
and their parts are not immediately obvious at first glance.
The photo at left points out the basic flower parts. The three
most conspicuous parts of the flower are actually the sepals,
the dorsal sepal often being a different color or pattern than
the two lateral sepals. The reproductive parts include the stigma
(female) in the center of the flower, and the two pollinia (male)
located in front of the dorsal sepal. Disa uniflora pollinia
are some of the largest in the orchid family, often 1 inch long.
The small petals are partly hidden behind the pollinia, and the
lip, usually the most conspicuous part of an orchid flower, is
a very small "tab" directly below the stigma.
First,
I built an insulated growing tray. The photo at left shows my
plywood tray, which has been lined with foil-coated foam insulation
board. The growing area of the tray has been made waterproof
by coating it with fiberglass and resin. The tray measures 26
inches by 48 inches. The tray sits atop a small chest-type freezer,
which has had its lid removed. The freezer is lined with a plastic
tarp, and filled with approximately 75 gallons of rainwater.
The freezer is plugged into a timer, which comes on for an hour
or two a day; enough to keep the water temperature approximately
50F. A small electric pump on a second timer, floods the tray
with cold water: Once a day for a few minutes during the winter,
and on and off for much of the day and night during very warm
weather. Constant flooding with water should be avoided, in order
to allow air to the roots. The water passes through a filter
before entering the tray, cleaning the water and adding vital
oxygen, and then drains directly back into the freezer compartment.
A digital thermometer is used to constantly monitor the temperature
of the water in the freezer.
If you
fertilize correctly, you should have nice tall leaves by the
time blooming season begins in May and June. (Notice in this
photo that my Disas are growing happily right next to my warmth-loving
Phalaenopsis.)| Diablo Disas | Website of Michael Gallagher of California. An extensive website with lots of excellent Disa information, photographs, and lists of species and the man-made hybrids. Summer 2004 Michael has given up Disas and moved to Thailand to study the terrestrial orchid genus Spathoglottis. But, he says his website will stay up indefinately. |
| Afrodisa | Website of Wally Orchard of Washington State. Again, lots of Disa information, photos, photos of Disas growing wild in South Africa, and trips abroad visiting Disa growers around the globe. He also produces the DisaPhile email newsletter. |